The present invention relates to a flame-retardant silicone oil composition, more particularly, to a flame-retardant silicone oil composition having greatly decreased combustibility and which is imparted with excellent self-extinguishability and heat resistance without affecting the excellent electrical properties and heat resistance inherent in silicone oils so as to be safely useful in respect of the as an insulating oil in electric instruments.
Several different types of electric insulation oils are known and have been used in electric instruments such as electric power cables, capacitors, transformers and the like, including mineral oils, phosphate ester-based oils, aromatic hydrocarbon oils, chlorinated synthetic oils, silicone oils, fluorocarbon oils and the like. The oils of each class have their own advantages and disadvantages. For example, mineral oils, aromatic hydrocarbon oils and silicone oils, in particular, having a relatively low viscosity are inflammable. Chlorinated synthetic oils have a toxicity problem. Flurocarbon oils generally have a relatively high specific gravity and thus cause an unavoidable increase in the weight of the electric instruments filled therewith, if not to mention the outstanding expensiveness of these oils as compared with the oils of other classes.
Silicone oils having a high viscosity are relatively flame-retardant but still are combustible enough to be classified as combustible oils by the glass tape test method specified in JIS C 2101. Flame retardance of silicone oils can be enhanced by compounding the oil with a flame retardant agent or combustion retarder compatible therewith as is proposed in Japanese Patent Kokai 49-39173, 51-20720 and 59-226408. The flame retardant agents proposed there are mostly organosilicone compounds with a few of fluorocarbon oils having relatively high vaporizability so that the flame retardancy imparted by compounding these agents is not maintained sustainedly over a long period of time. Several brominated compounds and phosphorus-containing organic compounds also have been proposed as a flame retardant agent but these compounds have problems of corrosiveness against metals and adverse influences on the electric properties of the oil compounded therewith as well as the instability of the flame retardance imparted thereby.